Tumblr will launch a test of "in-stream" ads on its desktop users' dashboards as soon as tomorrow, a source tells Business Insider. A company representative declined to comment.

The ads will look like normal posts from other Tumblr users, appearing in users' personal news feeds.

Previously, ads on Tumblr have been restricted to the "radar" and "spotlight" section of users' dashboards. Those positions are less intrusive and easily ignored by users.

In-stream ads, however, will appear as if they have come from someone a Tumblr user has followed. (When you follow someone on Tumblr, their blog posts are aggregated into your personal dashboard news feed.)

The ads are in "beta," according to a copy of the sales pitch deck obtained by BI. The program was clearly in the works prior to the Yahoo deal. A "select" group of advertisers will be chosen for the test. It includes:

An entry fee of $200,000.

Clients will get 10 "Radar" posts between May 21 and July 21

In addition, those clients get 10 web in-stream posts targeted at U.S. users.